This invention relates to an apparatus and methods for reducing in size an intraluminal medical device such as a stent, stent-graft, graft, or vena cava filter, and for introducing the medical device into the distal end of a delivery system for delivery of the medical device into the vasculature of a patient.
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Stents are available in both self-expanding and inflation expandable configurations. Inflation expandable stents are well known and widely available in a variety of designs and configurations. Both self-expanding and inflation expandable stents are typically crimped to their reduced configuration after being disposed about a delivery catheter. They are maneuvered to the deployment site and expanded to the vessel diameter either by fluid inflation of a balloon positioned between the stent and the delivery catheter, or upon release of the self-expanding stent from its crimped state, typically from a retaining sleeve or delivery sheath.
A number of techniques for crimping a stent to a balloon are used. One such technique that is commonly used in the radiological suite involves hand crimping the stent to the balloon. A stent is placed over an uninflated balloon and then squeezed with the fingers until the stent is in intimate contact with the uninflated balloon. The technique is highly operator dependent and can affect stent profile and stent placement with respect to the balloon and radiopaque markers. It can also affect the dilatation length of the stent and lead to pinching of the balloon.
Typically, mechanical stent crimping devices are either used to crimp the stent to the catheter prior to shipping the stent or in the radiological suite. In the latter case, the radiologist selects a bare stent with the desired properties and then mechanically crimps the stent to the desired balloon catheter.
Crimping and loading of self-expanding stents is often a more complicated procedure. Self-expanding stents are typically loaded into a constraining structure of a catheter delivery device after crimping of the stent. Stent loading typically involves pushing or pulling the stent out of a device in a constricted state and directly into a stent delivery system, or into an intermediary region and then into the delivery system. Alignment of the delivery system, typically the distal end of a catheter delivery device, with the crimping device can be problematic because the stent is relatively fragile, and typically the constrained outer diameter of the stent is only slightly less than the available inner diameter of the receiving delivery system or intermediate station. If the delivery system is not properly aligned with the crimping device, the stent and/or the catheter delivery system can be damaged. The constraining structure for the stent is typically a retaining sleeve or delivery sheath and is often in a tubular form. Damage may involve flaring of the ends of the catheter delivery system, or peeling or rolling of the tubing onto itself
Thus, there is a continuing need for improved devices and methods for loading a stent onto a delivery system such as a balloon catheter that are simpler, less expensive, more convenient, more reliable and avoid damage to the stent.